my 2 cockerels were together for about 3 months and there was no problem. but when they got sick I had to bring them in the house. one is in my bathroom and another one in the kitchen. I tried to bring them out for a while but the healthier one started to chase the weak one who used to be alpha cockerel! I had to bring him in. today I had the weak cockerel in my hands and went near the other one, he tried to attack him. but when I took that one and brought him to the bathroom where the weak one stays, my hero started to shake and didn't try to attack the other cockerel. it looks like it is all about territory. what can I do to reintegrate them to the flock so that they will not kill each other?
If you nursed them in separate rooms where they didn't see each other, you weakened the order they had established. When you put them out together the stronger one noticed the the other was weaker and now wants to become the top bird. The best you can do is to finish nursing them back to health, housed where they can see each other. Then let them sort it out. It may or may not be that they will get along again.